Direct-writing emulsions prepared by adding after silver halide precipitation in the presence of lead, insolubilizing acid anions, and heterocyclic nitrogen compounds

ABSTRACT

Direct-writing silver halide emulsions having higher maximum densities, lower background densities and increased image aging stability are prepared by precipitating silver halides in an acidified aqueous water-permeable colloid medium in the presence of a water-soluble plumbous salt, ripening the resulting emulsion in the presence of excess bromide ions, washing said emulsion to remove the soluble salts resulting from the precipitation of silver halides, adding a heterocyclic nitrogen compound and at least one acid anion capable of forming a substantially insoluble compound with lead ions, digesting the resulting emulsion, adding a halogen acceptor and coating the emulsion on a suitable support. The direct-writing, photodevelopable elements made from the emulsions are useful in oscillographs.

United States Patent Bigelow [451 Mar. 28, 1972 [54] DIRECT-WRITING EMULSIONS PREPARED BY ADDING AFTER SILVER HALIDE PRECIPITATION IN THE PRESENCE OF LEAD, INSOLUBILIZING ACID ANIONS, AND HETEROCYCLIC NITROGEN COMPOUNDS [72] Inventor: John Howard Bigelow, Rochester, N .Y.

[73] Assignee: E. I. du Pont de Nemours and Company,

Wilmington, Del.

[22] Filed: Oct. 10, 1969 211 App]. No.: 865,513

3,178,293 4/1965 Bigelow ..96/ 108 3,241,971 3/1966 Kitze ..96/108 3,287,137 11/1966 McBride ..96/107 3,409,436 11/1968 Farren et a]. .....96/94 3,418,131 12/1968 Bigelow ...96/108 3,451,817 6/1969 Bard et al. ...96/1 11 3,458,317 7/1969 Ditzer et al. ..96/108 Primary Examiner-Willard E. Hoag Attorney-Lynn Barratt Morris [57] ABSTRACT Direct-writing silver halide emulsions having higher maximum densities, lower background densities and increased image aging stability are'prepared by precipitating silver halides in an acidified aqueous water-permeable colloid medium in the presence of a water-soluble plumbous salt, ripening the resulting emulsion in the presence of excess bromide ions, washing said emulsion to remove the soluble salts resulting from the precipitation of silver halides, adding a heterocyclic nitrogen compound and at least one acid anion capable of forming a substantially insoluble compound with lead ions, digesting the resulting emulsion, adding a halogen acceptor and coating the emulsion on a suitable support. The direct-writing, photodevelopable elements made from the emulsions are useful in oscillographs.

8 Claims, No Drawings DIRECT-WRITING EMULSIONS PREPARED BY ADDING AFTER SILVER HALIDE PRECIPITATION IN THE PRESENCE OF LEAD, INSOLUBILIZING ACID ANIONS, AND I-IETEROCYCLIC NITROGEN COMPOUNDS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a process for making direct-writing, photodevelopable, oscillographic recording silver halide emulsions, layers, and elements having higher maximum densities, lower background densities and improved image aging stability.

2. Description of Prior Art Direct-writing radiation sensitive elements adapted for oscillographic recording and processes for preparing the silver halide emulsions for such elements are known. Improved types of such elements which are photodevelopable have been suggested in Hunt, U.S. Pat. Nos. 3,033,678; 3,033,682; Bigelow, U.S. Pat. No. 3,178,293. The Bigelow patent teaches that elements exhibiting high speed and image stability can be obtained by forming the silver halides in the presence of plumbous ions.

SUMMARY OF THE INVENTION This invention pertains to a process for making a directwriting, photodevelopable, colloid silver halide emulsion having improved photolyzed response and aging stability as indicated by reduced image access time and increased maximum density and lower background density. It has now been found that the above advantages are obtained if a silver halide is prepared with a water-soluble plumbous salt present at the time of silver halide precipitation, and after ripening but during or after the emulsion washing step, an anion capable of forming a substantially water-insoluble salt with the plumbous cation is added and during this addition or at a later period, e.g., just before or during digestion a heterocyclic nitrogen compound is added, and finally a halogen acceptor is added.

The heterocyclic nitrogen compound may also be added at the redispersing or digestion stage after the washing step. In general, the process comprises:

l. Precipitating a composition of silver halide containing at least 20 percent chloride in an aqueous acidified solution of a water-permeable organic colloid binding agent in a period of not more than 3 minutes in the presence of 5 to 20 mole percent of a water-soluble plumbous salt based on the silver halide at approximately 150-l80F;

2. Adding rapidly at least two times the stoichiometric amount of a water-soluble inorganic bromide necessary to convert the silver chloride to silver bromide, ripening F. emulsion by heating it to about 150-180F. forat least 3 hours, preferably adding from 5 to 20 mole percent of fine grain silver bromide containing -3 percent of silver iodide based on the originally precipitated silver halide during this ripening period;

3. Washing the emulsion with an aqueous solution to remove the soluble salts and during or just at the end of this step, adding to the emulsion based on the silver:

a. -25 mole percent of a stabilizing acid anion capable of forming a substantially water-insoluble plumbous salt, e.g., oxalate, sulfate, phosphate, iodate and carbonate, and/or b. 2-60 mole percent of a heterocyclic nitrogen compound containing at least two nitrogen atoms in the heterocyclic ring or the alkali metal salt thereof,

c. 0-15 mole percent of bromine in aqueous solution;

4. Redispersing the emulsion in an aqueous medium and, if desired, adding more water-permeable colloid, digesting the emulsion at about 1 l0l40F. for 5 to 30 minutes and, during digestion or prior to coating, adding based on the silver:

a. 0-5 mole percent of a water-soluble plumbous or cupric salt.

b. 0-120 mole percent of a water-soluble inorganic bromide.

c. a halogen acceptor; and

after digestion, the emulsion is cooled to a coating temperature, buffers and coating aids are added, and the emulsion coated on a suitable support to provide about 18-55 mg. of silver bromide per square decimeter.

The precipitation can be accomplished using any of the water-soluble silver salts and water-soluble halides described in the patents listed above but it is preferably carried out as claimed in U.S. Pat. No. 3,178,293 by admixing silver nitrate and a plumbous salt in an aqueous solution with an aqueous acidified solution of the colloid and a water-soluble halide. The water-soluble halide is preferably chloride but may contain small amounts of iodide and/or bromide ions. Suitable acids are hydrochloric, nitric and organic acids, e.g., citric, acetic, chloroacetic or bromoacetic acid.

Step (3) can be carried out by forming noodles and washing them, or by the coagulation and washing treatment described in Moede, U.S. Pat. No. 2,772,165 issued Nov. 27, 1965, especially in Example I.

An important aspect of the process of the invention involves the addition during the emulsion washing period of a stabilizing acid anion capable of forming a substantially water-insoluble plumbous salt.

By substantially insoluble it is meant that the lead salt has a solubility of not more than about 0.0050 gram in 100 milliliters of water at 25C. Another important aspect involves the addition of a heterocyclic nitrogen compound having at least two nitrogen atoms in the heterocyclic ring. It is also preferable to add up to 15 mole percent of bromine in aqueous solution. The addition of the above three ingredients increases the maximum density of the image and reduces the density of the background. It also greatly improves the aging stability of the element; that is, it improves shelf life.

The halogen acceptors include stannous chloride, salts providing iodide and thiocyanate ions, molecular iodine, alkali metal nitrite, phenylene diamines, aminophenols, hydroquinone, and 3-pyrazolidones, which are strong halogen acceptors but other halogen acceptors may be used.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred halogen acceptors of this invention are stannous chloride and potassium iodide. In general, from 05-120 mole percent and preferably 5-40 mole percent of a stannous salt based on the silver may be used or 0.2-2.0 mole percent of potassium iodide may be used. 'Rapid precipitation of silver chloride in the presence of 5-20 mole percent of plumbous salt, rapid conversion to silver bromide by the addition of at least two times the stoichiometric amount of soluble bromide salt with or without small amounts of a soluble iodide to convert the silver chloride to silver bromide or silver iodobromide (2.5 percent iodide) during this period are the basic preferred steps for making an emulsion suitable for treatment according to the invention. After the formation of the silver halide emulsion as described above, the emulsion is subjected to a washing treatment, preferably according to the coagulation process of the above Moede patent to remove the soluble salts resulting from the silver chloride precipitation and conversion to silver bromide. At the beginning of this step there is added the lead insolubilizing acid anion, and preferably at the end there is added the heterocyclic nitrogen-containing compound and the bromine. The heterocyclic nitrogen compound may also be added during the digestion step. The emulsion is redispersed, the halogen acceptor is added and the emulsion is digested. After this the usual coating adjuvants, e.g., hardeners, wetting agents, etc., are added and the viscosity is adjusted by the addition of a further quantity of gelatin or other colloid. Optical sensitizing dyes may be added in a manner well known in the art. In general, the ratio of gelatin to silver halide is 2:1 however, this is not at all critical. The prepared emulsion is then coated on a suitable support, e.g., paper and dried to give a dry coating weight equivalent of 18-55 mg. AgBr/dmF.

To determine the sensitometric characteristics of the direct writing material it may be exposed through a power of two step wedge in an electronic flash tube sensitometer similar to that described in Wyckoff and Edgerton, Journal of the Society of Motion Picture and Television Engineers, 66, 474 (1957). The instrument has a xenon discharge tube as the source of radiation and has available exposure times of l-l0,000 microseconds, e.g., 0.0000l0.01 second. The exposed material may be light-developed by irradiation under cool fluorescent lighting at intensities as shown in the following examples. To determine the densities of the image and background, a reflection densitometer may be used whose values correspond to visual density. To test image access time, the material was exposed at 0.001 second on an Edgerton, Germeshausen and Grier Mark Vl sensitometer and light developed by irradiation under cool white fluorescent lights. An arbitrary numerical designation of the time necessary for the image to appear is given with 1 being the fastest.

Examples II-XXVI below illustrate but are not intended to limit the scope of the invention.

EXAMPLE I (PRELIMINARY PROCEDURE) An emulsion was made in the following manner:

A. In a total volume of 2,500 ml. of an aqueous solution, there were dissolved 1.5 moles of potassium chloride, 50 grams of gelatin, 0.06 mole of plumbous nitrate and the pH was adjusted to 2 with 0.06 moles of hydrochloric acid. The temperature was adjusted to 160F.

B. In a total volume of 1,000 ml. of an aqueous solution, there were dissolved 1.5 moles of silver nitrate and0.l mole of plumbous nitrate.

C. While rapidly stirring, the silver nitrate solution was added to the aqueous silver chloride solution in 60 seconds or less.

D. During 60 seconds, there were added 4.8 moles of potassium bromide dissolved in 1,600 ml. of water. The resulting mixture was ripened by holding at 160 F. for 5 hours. Four hours after starting bromide conversion, in 30 seconds there was added 0.214 mole of a fine grain silver bromide emulsion prepared by precipitating on a mole for mole basis in an acidified aqueous gelatin solution silver bromide from silver nitrate and potassium bromide.

E. The resulting emulsion was coagulated and washed as described in Example I of Moede, U.S. Pat. No. 2,772,]65.

F. The emulsion was redispersed and there was added sufficient gelatin to provide a concentration of about 5-6 percent, 0.075 grams of the optical sensitizing dye, 3-ethyldihydrobenzoxazolylidine-Z:5 -isopropylidene-3-ethyl 2- TABLE I Test Method When NqSO. Added Coating Access ln gel ml! After AgCl ppm.

5% hr. before adding F. Gr. AgBr. 5: hr. after adding F. Gr. AgBr After coag. and pour off (just before wash) Test method No. l. Expose through power of two step wedge at 0.000! sec., on E.G.G. Sensitometer and photolyze 4 min.

IOO/E speed.

Image D measured above background density.

Background density ed above yzed r Dye density Density of emulsion layer measured above white paper.

Sample is exposed at 0.000! sec. on E.G.G. Sensitometer and photolyzed. Those showing image first when photolyzed are rated 1.

EXAMPLE II Example I was repeated except that the fine silver bromide emulsion added at stage (D) contained 2.5 mole percent iodide and there was added 0.3 mole of the heterocyclic nitrogen compound, 4-hydroxy-6-methyl-l,3,3a,7-tetrazaindene, in aqueous sodium carbonate solution (15 grams in 100 ml. of 1M Na CO at the end of the washing step (E). Na SO gives reduced background density. (Note especially the poor response when Na SO is present in the gel salt where prior art adds H SO in presence of Pb).

TABLE II Coating No.

Moles Naesot 1.6 moles of- Where added in steps silver of process of Ex. I

None

0. 2 A. 0. 2 Just before D. 0. 2 hr. before F. gr.

AgBr addn. in step D. 0. 2 hr. after F. gr. AgBr addn. in step D. 03 0. 2 After coag. and pour at! at end of Step E. 05 No N8zSO4 and no heterocyclic nitrogen. compound.

.decimeter. and dried in a conventional manner.

in this example. only one of the three important ingredients, namely the stabilizing lead insolubilizing acid anion, sodium EXAMPLE lll Example I was repeated adding 0.1 mole of the heterocyclic nitrogen compound of Example ll after washing and 0.2 moles of sodium sulfate added at the start of the washing step.

In addition to the regular photolysis at about 95 foot candles intensity, a rapid photodevelopment was carried out at a higher intensity.

The results show that sodium sulfate with the heterocyclic nitrogen compound produces greater speed, contrast (lower background density), and resistance to blast photolysis, a

sulfate, was added at different stages of the making procedure method of rapid development.

l Expose through power of 2 step Wedge at 0.0001 sec. on E.G.G. Sensitometer. and photolyze at 350 It. candles fluorescent light for 1 minute.

2 Background density: 1 shows lighter density. 2 darker.

3 The greater number of steps shows greater speed.

EXAMPLE 1V EXAMPLE V Example I was repeated and the amount of plumbous salt added at silver halide precipitation, and the amount of sulfate or oxalate anion, the amount of the heterocyclic nitrogen compound of Example 11, and the amount of bromine is shown in the following table. The sulfate or oxalate anion (as sodium sulfate or sodium oxalate) was added at the start of washing,

and the heterocyclic nitrogen compound and the bromine were added at the end of the washing period (step E). The halogen acceptor added in step (F) was 20 mole percent of stannous chloride based on the silver halide. This Example shows that the ingredients added at step E all contributed to aging stability. The five controls indicate that aging lowers E mpl I was pea ed P 10 1 8 a g at Stage (E) speed, maximum density and increases background density.

TABLE V Moles Total 804' Fresh Over aging tests moles Cr /L5 Hetero- Pb+ /1.5 mole Ag nitrogen S D B D.D S D B D.D. mole Ag+ halide compound G. Br Coating No. controls:

29 .14 .03 107 20 .14 .03 36 .13 02 126 .24 16 02 37 22 03 126 28 26 03 36 18 03 126 .27 21 .02 .34 10 04 163 29 .18 .02 35 25 02 126 27 26 02 21 31 .18 02 126 .28 .22 03 .21 .37 17 .02 126 .31 .23 .02 .21 29 .14 .02 12s .23 .20 .03 .21 0.2 so.- (1895 .35 .14 .02 107 .28 .23 .02 21 0.2 804- 0. 895

7 Aged 7 days at 120? and 70% relative humidity (equivalent to approx. 10 mo. natural age).

0.2 mole of sodium sulfate, 0.1 mole of the heterocyclic nitrogen compound of Example 11, and bromine as indicated in the following table. In place of stannous chloride in stage (F) as the halogen acceptor there was used 0.33 mole percent of potassium iodide based on the silver halide. The emulsion was digested 20 minutes at 110F. Addition of bromine at the end of make gives reduced background densities and thereby greater contrast. Useful amounts cover the whole range tested.

TABLE IV Make Variation Test Method No. l Coating No. Sp. D, Bkgd. g. Br lrnole of Ag 1 126 0.25 0.11 None As photolysis continues those samples containing greater amounts of bromine continue to show reduced background densities.

EXAMPLE VI Example 1 was repeated and amounts of the heterocyclic nitrogen compound, 4-hydroxy-6-methyl-l,3,3a,7-tetrazaindene were added at the end of step (E) as indicated in the following table. The results show a useful concentration range of this compound.

Example 1 was repeated except that oxalic acid was added at the start of the washing period as the stabilizing acid anion in place of sodium sulfate in the amounts shown in the table. The results are shown below.

TABLE VII [Exposed on E61. G. sensitometer at 0.0001sec.]

"Blast" photolysis at Photolysed at ft. candles 300 it. candles Moles Coating No. Access Bkgrd. Speed 1 Bkgrd. Speed 1 Ag halide 1 Number of steps visible. Greater number equals greater speed.

1 As photolysis continued hiflhg l than;

(observed at 1 hr.), the background of these coatings remains EXAMPLE V111 Example V was repeated except 0.33 mole percent of potassium iodide based on the silver halide was added in stage (F) in place of stannous chloride as the halogen acceptor. In addition the fine grain silver bromide emulsion added at stage (D) contained 2.5 mole percent iodide. The quantities of sulfate anion, heterocyclic nitrogen compound (of Example 11) and bromine per 1.5 moles of silver halide are shown in the following table.

EXAMPLE X Following the preliminary procedure of Example 1, the silver halide was formed in the presence of 14 mole percent of plumbous nitrate based on the silver halide at pH of 2 (step C). Potassium bromide in an amount of 3.2 times the stoichiometric amount to convert substantially all of the silver chloride to silver bromide was added and the emulsion was ripened for 5 hours during which time 14 mole percent of fine grain silver bromide based on the silver halide formed at TABLE VIII Emulsion process variations Test method #1 Moles Oven aging tests Moles hetero Fresh (see Ex. V) N 82804/ N-oornpound Gr. Bt'z/ 1.6 moles 1.5 moles 1.5 moles D B D.D. S D B D.D. Ag halide Ag halide Ag halide 30 08 04 33 18 16 .04 0.1 30 10 .04 95 21 .04 0. 1 1.79 31 09 04 107 22 12 04 3 32 09 04 64 21 14 04 0. 1 o 31 09 .06 64 14 04 0. l l. 79 31 0B 06 126 23 10 04 0.3 1. 79

These data show that a combination of Pb insolubilizer, hetero-N-compound, and Br produce the best results in terms of higher speed, maximum density and lower background, and also better aging stability.

precipitation was added. At the beginning of step (E) there 25 was added 13.3 mole percent of sodium sulfate and at the end of the washing stepthere was added 6.6 mole percent of the following heterocyclic nitrogen compounds.

- solution (A) contained 80 percent potassium chloride and 20 EXAMPLE 1X Following the procedure of Example 1 an emulsion was percent potassium bromide. The silver halides were 0 precipitated in the presence of 14 mole percent of plumbous salt in an aqueous gelatin medium, the pH of which was adjusted to 2 with hydrochloric acid. in step (D) of the (|3=O procedure of Example 1 there was added 3.2 times the I stoichiometric amount of potassium bromide to convert substantially all of the silver chloride to silver bromide and then there was added 14 mole per cent of a fine grain silver bro- *kembenkblmflazine mide emulsion as indicated in the table and 0.5 mole percent 0 of potassium iodide. At the beginning of step (E) there was i g added 13.3 mole percent of oxalic acid as indicated in the table and at the end of the washing step there was added 20 1 mole percent of 4-hydroxy-6-methyl-l ,3,3a,7-tetrazaindene of Z Example 11 based on the. silver halide and 2.3 grams of N bromine per mole of silver. in stage (F) there was added 0.33

mole percent of potassium iodide and 5 mole percent potassi- 4'kem-Lmethy14'35-mazm" um thiocyanate based on the silver halide. The emulsion was digested 20 minutes at 1 10F. The results are as follows:

TABLE [X f HC\ l III Test Method No. l' W QPL Coating Fine grain Nov speed D'W Background ABE HCIO 4. Tetrahydro-5-methyl-2-keto-l,3,5-trlaz1ne l 1 213 0.32 0.14 Yes Yes /2 2 213 0.34 0.15 Yes No a 251 0.33 0.12 No Yes BN1 3NH 4 305 0.33 0.16 No No H206 40H:

5 These data show that the presence of oxalic acid at start of wash produces lower background 1n the 1od1de halogen accep- 5 Dimemyl 01 t etrahy thyljzke W113, mine tor system.

1. Exposed at 0.0001 second on E.G.G. Sensitometer and H photolyzed 4 minutes at 50 feet candles intensity. 7 g\ Speed 100/5, Homo-N1 at|-IcH,0H D,,,,,, maximum density measured above background H206 40H:

density, 5 Background density measured above unexposed but f photolyzed area.

6. 4-hydroxy-6-rnethyl-l,3,3a,7-tetrazaindene Step (F) was carried out as shown in Example I. Usingstannous chloride as the halogen acceptor. The results are shown in the following table.

TABLE X Photolyzed Response 7 3a,7-tetrazaindene The data show that D is improved by the several N-bearing compounds.

EXAMPLE Xl Example X was repeated using at the end of the washing step (E) 10 mole percent based on the silver halide of the following heterocyclic nitrogen compounds.

1. 4,6dihydroxy-2-methyl pyrimidine 2. Z-hydroxy benzimidazole 4. 2-hydroxy-4-methyl pyrimidine hydrochloride The results are shown in the following table which indicate higher maximum densities and generally lower background Example X was repeated using the heterocyclic nitrogen compound, 7-chloro-4-hydroxy-l ,2,3-benzotriazine,

and 4-ketobenz-l,2,3-triazine shown in Example X in the amounts shown in the following table.

TABLE Xll Photolyzed Response Coating Mole No. Speed D Bkgd Amt. Compound I 226 0.30 0.12 None 2 213 0.32 0.11 2.96 7-chloro-4- hydroxyl .2.3- benzotriazine 3 213 0.32 0.11 6.66 d-ketobenzl ,2,

3-triazine These data show that a combination of Pb insolubilizer, hetero-N-compound, and Br: produce the best results in terms of higher speed, maximum density and lower background, and also better aging stability.

EXAMPLE Xlll Example X was repeated except that the aqueous gelatin alkali metal halide salt solution contained percent chloride and 20 percent bromide as the halide composition. The fine grain silver bromide in an amount of 14 mole percent and 0.25 mole percent potassium iodide based on the silver halide formed at precipitation was added or not added during ripening (step D) as indicated in the table. At the start of the washing step (E) there was added 13.3 mole percent of oxalic acid as indicated by the table. At the end of the washing step there was added the pyrimidines and the heterocyclic nitrogen compound, 4-hydroxy-6-methyl-l ,3,3a,7-tetrazaindene in the amounts shown in the table all based on the silver halide formed in step (C).

1.1 2 These data show that 2-hydroxy-4-methyl pyrimidine compounds as shown in the following table and adding 0.33 hydrochloride, and 4,6-dihydroxy-2-methyl pyrimidine give mole percent of potassium iodide during the digestion step response similar to 4-hydroxy-6-methyl-l,3,3a,7-tetrazain- (F).

TABLE XIII Photolyzed response Ctg. F. gr. I- at Mole,

. D B AgBr Ripg. H2Cz04 percent Compound added .42 .18 20 2-hydroxy-4-methyl pyrimidine hydrochloride.

.39 .17 20 4,6-dihydroxy-2-methyl pyrimidine.

.39 19 20 2-hydroxy-4-methy1 pyrimidine hydrochloride.

.38 .18 20 4,6-dihydroxy-2-methyl pyrimidine.

.40 .22 Yes... Yes... Yes. 20 4-hydroxy-6-methy1-1,3,3a,7-tetrazaindene.

.40 .20 Yes-.. Yes... Yes-.. 60 Do.

dene. Although excellent response is obtained with TABLE XV pyrimidines in the absence of fine grain AgBrand I at ripening and oxalic acid at the start of wash, slightly greater D 20 and lower background are obtained in their presence. Phoiolyzed 7 Response Added at Make XIV Ctg. No. PM, Bkgrd Amount Compound An emulsion was made according to Example X except that I 035 M movie the fine grain silver bromide was omitted during the ripening l,3,3a.7 t eirazaindene. step (D) but potassium iodide in an amount shown in the table 2 016 10 2-hydmybsnzimidamk was added during this step. No stabilizing acid anion was 3 added during the washing step '(E) and the heterocyclic I nitrogen compounds, 4-hydroxy-6-methyl-l,3,3a,7-tetrazain- These-data show that 4-hydroxy-6-methyl-l,3,3a,7-tetrazaindene and 2-hydroxy-4-methyl pyrimidine hydrochloride were dene and 2-hydroxybenzimidazole produce greater added as shown in the table. photolyzed D,,,,,,.

TABLE XIV Photolyzed Compound added response Ctg. Mole percent Halogen No. S D B I- at ripg. Amt. Name acceptor 1 251. .36 .15 .025 20 mole percent- 4-hydroxy-6-methyl-1,3,3a,7- (Sn system).

tetrazaindene. 2 261 .36 .16 do do Do. 3 251 .37 l5 7 .do 2-hydroxy-4-methyl Do.

rimidine hydrochloride.

4 126 .36 .16 11 Do. 6 319 .33 .12 Do. 6 201 .34 14 Do These data show that both heterocyclic nitrogen compounds EXAMPLE XVI ve otol zed D mpro ph y Example 1 procedure was carried out with the variations in the aqueous gelatin salt composition, (A) the addition of 4- EXAMPLE Xv hydroxy-o-methyl-l,3,3a,7-tetrazaindene and bromine at the end of the washing step as shown in the following table. These results show:

Example XIV was repeated adding 0.5 mole per m 0 1. Lower background darkening and greater speed occur potassium iodide during ripening and heterocyclic nitrogen with some Br in the original gelatin solution than with all TABLE XVI Emuisioiglgrocess variations, 4-hydroxygelatinalimetai halide 6-methy1- 1,3,3a,7- B a, Ctg. K01, KBr, B20204, tetrazaindene, g./ Halogen No. S D B percent percent mole percent mole percent mole Ag acceptor 1 107 .32 26 100 (Sn system). 2.- 188 .87 .24 Do. 3 188 .37 22 4.- 213 .37 17 5 213 .38 18 6., 163 .36 18 7 )5 .29 12 8., 163 .33 13 9 163 .33 12 10 188 .31 08 ll... 18H .36 0) 3 l 213 36 01) 3 CI in both Sn and l halogen acceptor systems.

2. 4-hydroxy-6-methyl-l,3,3a,7-tetrazaindene produces greater D in both Sn and l halogen acceptor systems.

3. Bromine produces lower background density with all Cl in the original gelatin solution when employed in the Sn system, but is not necessary if some Br" is present in the original gelatin solution or if using the I halogen acceptor system.

4. The Pb insolubilizer, oxalic acid reduces background density with all Cl at precipitation in the stannous halogen acceptor system.

In preparing the acidified aqueous gelatin alkali metal halide solution of step (A) in Example 1 above, it is preferable to use hydrochloric acid as the means of lowering the pH rather than sulfuric acid or other acid, the anion of which would form a substantially water insoluble salt with the plumbous ion. The presence of the stabilizing acid anion in the gelatin salt composition as shown in Example I gives definitely poorer photolyzed response. This is indicated by higher backgrounds, lower maximum densities and speeds. By adding these stabilizing anions at a later stage, preferably just before washing stage, the above difficulties are overcome particularly when used in association with a heterocyclic nitrogen compound of the type set forth above, and with bromine. The stabilizing acid anions serve to reduce undesirable background densities, particularly upon aging, i.e., they improve shelf like; The heterocyclic nitrogen compounds generally produce greater maximum densities but also improve the photolytic response and aging stability. These compounds may be added as alcohol solutions or dissolved in aqueous alkaline solutions. Bromine serves to reduce sensitivity to low intensity photolyzing light, i.e., to reduce background density, and to improve aging stability.

Stannous chloride, when used as a halogen acceptor, may be added from aqueous solution, particularly when such solutions are made using the anhydrous stannous compound; however, the stannous salt may also be added from ethanol, 2- ethoxyethanol, glycerine, dilute hydrochloric acid, etc.

Where it is desired, other halides or combinations of halides may be used to form the silver halide grains. For example, pure silver chloride, silver chlorobromide, silver iodochloride or silver chlorobromoiodide may be used. When soluble chloride salts are used, it is desirable, because of solubility differences, to form the silver halide grains of desired size and then add sufiicient soluble bromide salts to provide the desired concentration of bromide ions.

Other optical sensitizing dyes in addition to that disclosed in Example I, such as those disclosed in Hunt, U.S. Pat. No. 3,189,456 can be added along with buffering compounds and coating aids.

In place of the gelatin binding agent used in the foregoing examples there can be substituted other natural or synthetic water-permeable organic colloid binding agents. Such agents include water-soluble or permeable polyvinyl alcohol acetates, polyvinyl ethers, and acetals containing a large number of extra linear CH CHOH groups; hydrolyzed interpolymers of vinyl acetate and unsaturated addition polymerizable compounds, for example, maleic anhydride, acrylic and methacrylic acid esters and styrene. Suitable colloids of the last mentioned type are disclosed in U.S. Pat. Nos.

2,276,322; 2,276,323 and 2,397,866. The useful polyvinyl acetals include polyvinyl acetaldehyde acetal, polyvinyl butyraldehyde acetal and polyvinyl sodium o-sulfobenzaldehyde acetal. Other useful colloid binding agents include the polyvinyl lactams of Bolton, U.S. Pat. No. 2,495,918, e.g., poly-N- vinylpyrrolidone; the hydrophilic copolymers of N-acrylamido alkyl betaines described in Shacklett, U.S. Pat. No. 2,833,650 and hydrophilic cellulose ethers and esters.

Suitable supports for the photographic emulsions made by the novel process of this invention include those used in the prior art on oscillographic recording elements. The preferred support is a photographic grade paper but it may be a hydrophobic film composed of a cellulose ester, e.g., cellulose acetate or a polymer, e.g., polyester films disclosed in Alles et al. U.S. Pat. No. 2,627,088 and Alles, U.S. Pat. No. 2,779,684.

The novel process of this invention produces photodevelopable, direct-writing radiation sensitive emulsion layers and elements having several advantages over the prior art products. The emulsion layers and elements upon exposure to high intensity radiation and subsequent photodevelopment, yield images of higher maximum density and lower background density than are obtainable with direct writing elements known heretofore. In addition, the image access time is greatly reduced as compared to the recording elements of the prior art. Aging stability has also been improved.

The elements may be subjected to relatively high intensity illumination for long periods of time without substantial change in the image characteristics. The elements can be used to reproduce photographically the image record by high-intensity exposing radiation and without serious image deterioration. The elements have'high photographic speed and contrast and, in addition, they have the ability to produce a useful image using relatively high intensity photolyzing light.

The elements are extremely convenient to use because wet processing can be eliminated; however, the elements are adaptable to conventional chemical development and fixing when a halogen acceptor other than tin is used. When water soluble stannous compounds are used as halogen acceptors, an acid developer may be used to develop the image.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for preparing a direct-writing, photodevelopable colloido-silver halide emulsion which comprises:

1. precipitating silver halide containing at least 20 percent silver chloride in an aqueous acidified solution of a waterperrneable organic colloid binding agent at about l50-l80 F. during a period not more than 3 minutes in the presence of 5-20 mole percent of a water-soluble plumbous salt; I 2. admixing at least two times the stoichiometrlc amount of a water-soluble inorganic bromide to convert silver chloride to silver bromide and ripening the emulsion at l50-l F. for at least 3 hours;

. washing the emulsion with an aqueous solution to remove the soluble salts, and during or after the washing step adding to the emulsion based on the silver:

a. 5-25 mole percent of a water-soluble compound containing a stabilizing acid ion capable of forming a water-insoluble salt with the plumbous ion, and

b. 2-60 mole percent of a heterocyclic nitrogen compound containing at least two nitrogen atoms in the heterocyclic nitrogen ring or an alkali metal salt of said nitrogen compound, and I c. 0-15 mole percent of bromine in aqueous solution;

4. redispersing the emulsion in an aqueous medium, adding additional water-permeable colloid and digesting the emulsion at l l0-l40 F. for 5-30 minutes and during or after the digesting step, adding, based on the silver:

a. 05 mole percent of a water-soluble plumbous or cupric salt,

b. 0-120 mole percent of a water-soluble inorganic bromide, and

c. a halogen acceptor.

2. A process according to claim 1 wherein during step 2 there is admixed with the emulsion from 5-20 mole percent of fine-grain silver bromide which contains 0-3 percent of silver iodide based on the original precipitated silver halide.

3. A process according to claim 1 wherein the water-soluble compound of step 3(a) is sodium sulfate.

4. A process according to claim 1 wherein the water-soluble compound of step 3(a) is sodium oxalate.

5. A process according to claim 1 wherein the heterocyclic nitrogen compound of step 3(b) is 4-hydroxy-6-methyl-l ,3,3 a-7-tetrazaindine.

6. A process according to claim I wherein the halogen acceptor is stannous chloride.

7. A process according to claim 1 wherein an optical sensitizing dye is admixed with the emulsion.

8. A direct-writing, photodevelopable photographic paper bearing a layer of emulsion prepared according to the process of claim 1 

2. A process according to claim 1 wherein during step 2 there is admixed with the emulsion from 5-20 mole percent of fine-grain silver bromide which contains 0-3 percent of silver iodide based on the original precipitated silver halide.
 2. admixing at least two times the stoichiometric amount of a water-soluble inorganic bromide to convert silver chloride to silver bromide and ripening the emulsion at 150*-180* F. for at least 3 hours;
 3. washing the emulsion with an aqueous solution to remove the soluble salts, and during or after the washing step adding to the emulsion based on the silver: a. 5-25 mole percent of a water-solubLe compound containing a stabilizing acid ion capable of forming a water-insoluble salt with the plumbous ion, and b. 2-60 mole percent of a heterocyclic nitrogen compound containing at least two nitrogen atoms in the heterocyclic nitrogen ring or an alkali metal salt of said nitrogen compound, and c. 0-15 mole percent of bromine in aqueous solution;
 3. A process according to claim 1 wherein the water-soluble compound of step 3(a) is sodium sulfate.
 4. A process according to claim 1 wherein the water-soluble compound of step 3(a) is sodium oxalate.
 4. redispersing the emulsion in an aqueous medium, adding additional water-permeable colloid and digesting the emulsion at 110*-140* F. for 5-30 minutes and during or after the digesting step, adding, based on the silver: a''. 0-5 mole percent of a water-soluble plumbous or cupric salt, b''. 0-120 mole percent of a water-soluble inorganic bromide, and c''. a halogen acceptor.
 5. A process according to claim 1 wherein the heterocyclic nitrogen compound of step 3(b) is 4-hydroxy-6-methyl-1,3,3a-7-tetrazaindine.
 6. A process according to claim 1 wherein the halogen acceptor is stannous chloride.
 7. A process according to claim 1 wherein an optical sensitizing dye is admixed with the emulsion.
 8. A direct-writing, photodevelopable photographic paper bearing a layer of emulsion prepared according to the process of claim
 1. 